The present invention relates to an improved method for heating a thermal shrinkage tube to effect shrinkage when the tube is applied to reinforce the splice portion between optical fibers or the like, and an improved device used for performing the method.
Conventionally, a plurality of heaters have been used for heating a thermal shrinkage tube so as to cause shrinkage in the tube, for example, so as to protect the splice portion between optical fibers.
In such a case, if air bubbles remain in the space between the fiber splice portions and the inner surface of the tube, the optical transmission loss due to the splice portion becomes large. Therefore, it is necessary to make the inner surface of the tube adhere closely to the splice portion so as to completely purge the air bubbles. To this end, after the splice portion has been covered by a thermal shrinkage tube, the tube is first heated so as to increase the temperature at the central portion thereof to thereby cause the inner surface of the tube to adhere closely to the splice portion to provide thereat a state including no air bubbles and then the heat is successively progressively applied to the opposite ends of the tube to thereby remove air bubbles therefrom.
In the case where, for example, wire heaters are used as the heating means for performing the above-described method, a method has been conventionally used in which three wire heaters are longitudinally separately provided along the thermal shrinkage tube covering the splice portion, so that the central wire heater is first energized to thereby cause the tube to shrink at its central portion to closely adhere to the splice portion to remove air bubbles therefrom, and then the shrinkage is made to successively progress from the central portion to the opposite ends of the tube by a time-difference heating system to thereby cause the tube to entirely closely adhere to the splice portion with no air bubbles remaining inside the tube. In the conventional method, however, it is necessary to provide not only three separate wire heaters, but also three temperature rise control devices such as thermistors, so that various disadvantages arise in that the control circuit becomes complex, thereby requiring additional component parts and resulting in an increased cost in performing the method and in providing the device for achieving the method.